I was hoping someone might be able to share some troubleshooting pointers regarding my inoperable heating and defrosting system. I'm the original owner of an '02 F-250 7.3L diesel. The air conditioning works fine, but I'm not getting any warm air on any of the heating or defrost settings - doesn't matter how long I wait.

A few more bits of information:

- The blower motor is running strong.

- The blower motor properly responds to fan speed setting changes.

- The actuators that route the air flow to the various vents depending on the heater/defroster **** setting appear to be working properly.

- I swapped out the air flap temp door actuator behind the glove box, but that didn't help. It's a little hard to see up inside the dash, but it didn't appear as though the new actuator was doing anything when I would switch over from a/c to heat and vice versa.

- I'm in SoCal, so the heater/defroster often sits unused for extended periods of time. Unfortunately though, when you need it, you need it.

Is there anything else simple you guys can think of (maybe a relay on the fuse panel?) that I could check myself before I'm forced to take her in and incur the cost of the mechanic's shop? I'm somewhat mechanically oriented, but have little to no experience on the automotive side of things. Changing out the air conditioner/heater door actuator was pretty easy for me, but I wouldn't have attempted even that were it not for a very clear and informative youtube video.

 

1. Did you check to see if coolant was even circulating through the heater core? No hot coolant flow = no heat.

2. The temperature blend door actuator responds only to the temperature control ****, the mode selector switch doesn't do anything as long as it's not in the OFF position.

See the HVAC FAQs in the HVAC section, they also apply to the Super Duty line.

 

Thank you for taking the time to respond to my questions. Being an extreme novice at this shade tree mechanic thing, I'm afraid I wouldn't know how to check for proper coolant flow to the heater core. I'll do some more searching online to see if I can find a video addressing that issue. I can tell you that when I was swapping out the blend door actuator last night (after having just driven home from work) there were plenty of very warm components in that general area behind the glove box. Not anything that would burn you on contact, just structures primarily to the right and above the flap actuator that were uncomfortably warm to touch.

As to your point #2 above, I made sure the temp control **** was turned all the way to hot before attempting to verify the proper operation of the blend door actuator. Nevertheless, when switching from air conditioner mode at a cool temp setting, to heater mode at a full hot temp setting, I didn't detect any movement of the actuator arm.

 

Check the hater hoses when truck is cold, then start it. When it is up to temp both hoses should be hot. I don't know if the 7.3 has a vacuum shut off valve inline with heater or not, just follow the hoses between engine and heater core, if it does, with truck running and warm see if you have hot hoses on both sides of it , if not remove vacuum line and see if the valve moves, if it doesn't you may have a bad valve, if it does and you have both heater hoses hot when up to temp you either have a partially plugged heater core, they sometimes get a "coating of scum" on the inside that seems to insulate them so the air going through doesn't pick up much heat, you may or may not be able to flush well enough to fix but most likely will need a new one, or the problem is in the heater box itself not directing the air through the core.

 

You're not supposed to. As noted, the blend door actuator only responds to the temp control setting, not the mode setting. Leave the mode setting in any position except OFF, and evaluate ONLY the temperature control.

 

Many thanks to both of you for your patience in helping walk me through this.

 

Update:

Well, it turns out the heater core was blocked up solid and my water pump has been inoperative for God only knows how long.

As painful as this was to the wallet, I'm amazed that these trucks can run for months (or years?) with no coolant circulating through the engine block.

 

The radiator was fine? Not clogged up as well? Did you take this to a shop to get it fixed?

 

That was the first thing I thought as well, Deuce. If deposits had blocked the heater core, wouldn't replacing it without checking the radiator risk having the new one clog right back up again? Fortunately I took my truck to a local family owned and operated shop that specializes in diesel pickups and has a very good reputation amongst the area car enthusiasts. As part of the cost of the service, they checked the integrity of the radiator (which was fine) and did a flush and refill just to be on the safe side. I'm a stickler about replacing fluids at the prescribed intervals, so I wasn't too surprised that the radiator was in good shape.

The water pump apparently failed because the impeller blade itself was moving down the splined shaft and grinding into the housing body. New hoses, clamps and thermostat pretty much rounded out the service.

 

JJ, just as an FYI, I asked the mech about that and he said that on our 7.3s, there is no shut off valve to the heater core. The engine coolant circulates through it whenever the engine is running. He said that the 6.0s and later do have this shut off mechanism.

 

I wasn't sure on the 7.3's as my buddy's '03 7.3 does have one but it could have been added. A thought though is even if the water pump impeller was loose on the shaft it had to be circulating enough coolant to prevent overheating,if it had none, the engine would have overheated. If you are going by the dash gauges, they are very inaccurate at best, they are not truly an analog gauge they are a glorified idiot light. You could have been running hot, just not quite hot enough for the gauge to trigger the next level on the needle. You need to have something like a ScanGauge 2 or Torque Pro app for your cell and a bluetooth dongle to know what truly is happening. Probably more important on the 6.0 but still a very good idea on the 7.3.